LM5033SD-EVAL National Semiconductor, LM5033SD-EVAL Datasheet - Page 11

• Manufacturer Part Number: LM5033SD-EVAL
• Description: BOARD EVALUATION LM5033SD
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of LM5033SD-EVAL

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 9V
• Current - Output: 20A
• Voltage - Input: 40 ~ 60V
• Regulator Topology: Buck
• Frequency - Switching: 315kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LM5033
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Power - Output: -
• Lead Free Status / Rohs Status: Not Compliant

Application Information
PC BOARD LAYOUT
The LM5033 current sense and PWM comparators are very
fast, and as such will respond to short duration noise pulses.
Layout considerations are critical for the current sense filter.
The components at pins 3, 8, 9, and 10 should be as
physically close as possible to the IC, thereby minimizing
noise pickup in the PC tracks.
If a current sense transformer is used both leads of the
transformer secondary should be routed to the sense filter
components, and to the IC pins. The ground side of the
transformer should be connected via a dedicated PC board
track to pin 7 of the IC rather than through the ground plane.
If the current sense circuit employs a sense resistor in the
drive transistor sources, a low inductance resistor should be
used. In this case all the noise sensitive low power grounds
should be connected in common near the IC, and then a
single connection made to the power ground (sense resistor
ground point).
The outputs of the LM5033, or of the high voltage gate driver
(if used), should have short direct paths to the power MOS-
FETs in order to minimize the effects of inductance in the PC
board traces.
If the internal dissipation of the LM5033 and any of the power
devices produces high junction temperatures during normal
operation, good use of the PC board’s ground plane can help
considerably to dissipate heat. The exposed pad on the
bottom of the LLP-10 package can be soldered to ground
plane on the PC board, and the ground plane should extend
out from beneath the IC to help dissipate the heat. The
exposed pad is internally connected to the IC substrate.
(Continued)
FIGURE 3. Deadtime Adjustment
11
Additionally, the use of wide PC board traces where possible
can help conduct heat away from the IC. Judicious position-
ing of the PC board within the end product, along with use of
any available air flow (forced or natural convection) can help
reduce the junction temperatures.
APPLICATION CIRCUIT EXAMPLE
Figure 6 shows an example circuit for a half-bridge 200W
DC/DC converter built in a quarter brick format. The circuit is
that of an intermediate bus converter (IBC) which operates
open-loop (unregulated output), converting a nominal 48V
input to a nominal 9.0V output with a 30 mΩ output imped-
ance. The current sense transformer (T2), and the associ-
ated filter at the CS pin, provide overcurrent detection at
approximately 23A. The auxiliary winding on T1 powers V
and the LM5100’s V+ pin (once the outputs are enabled) to
reduce power dissipation within the LM5033. The LM5100
provides appropriate level shifting for Q1. Synchronous rec-
tifiers Q3 and Q4 minimize conduction losses in the output
stage. Dual comparators U2 and U3 provide under-voltage
and over-voltage sensing at Vin. The under-voltage sense
levels are 37V increasing, and 33V decreasing. The over-
voltage sense levels are 63V increasing, and 61.5V decreas-
ing. The circuit can be shut down by taking the ON/OFF input
below 0.8V. An external synchronizing frequency can be
applied to the SYNC input. Measured efficiency and output
characteristics for this circuit are shown in Figure 4 and
Figure 5.
20035416
www.national.com
CC